Copper, copper complexes, and copper/nickel alloys are known to have marine anti-foulant properties. In particular, bottom paints for boat hulls have been developed that include copper complexes in a semi-water permeable paint. The copper complexes leach out of the paint into the surrounding water layer during use. While effective at inhibiting marine bio-fouling, these paints also are a source of undesirable toxic contamination for surrounding waters.
Copper/nickel alloy boat hulls have also been constructed on an experimental basis, and have been found to be effective in prohibiting fouling. However, such hulls are prohibitively expensive to produce.
Improved bottom-paint coatings have been developed and tested in recent years that include copper/nickel alloy particles suspended in a two-part epoxy resin mixture. These copper/nickel-epoxy mixtures have been found effective as potentially inhibiting marine bio-fouling, and also serve as a corrosion inhibitor and mechanical protective coating. However, such coatings have utilized epoxy systems that include an epoxy resin prepolymer and a polyamine hardener, i.e., crosslinking agent, to cure the prepolymer. These polyamine-based epoxy-copper/nickel coating systems have not met with large commercial success because of difficulties in handling the resin. Epoxies generally exhibit exothermic cure cycles, and thus cure most rapidly in large quantities due to the increased thermal mass.
As a practical effect, the "pot-life" of conventional polyamine-based epoxy coatings has been found to be unsatisfactorily short. As used herein, "pot-life" refers to the duration of time during which the mixed resin (i.e., mixed resin prepolymer and hardener) remains workable, having a satisfactory viscosity for spray application. The mixed resin tends to rapidly increase in viscosity and may cure while still within the mixing container before application is complete. When the resin is dispersed by spraying, the resin may cure within the spray gun, resulting in the loss of expensive equipment. A further drawback of polyamine-based systems is that once the liquid resin has been applied as a film, curing of the resin film proceeds at a much slower pace. This is due to the decreased thermal mass of the sprayed film and conductive and convective heat losses. Because of the slow cure in the thin film stage, the thickness of film that can be applied is limited. Film substantially thicker than 10 mils tend to sag or sheet while still liquid during cure, resulting in an inconsistent final coating thickness.